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Distinguishing causes of virulence evolution

smith j (2011) Distinguishing causes of virulence evolution: Reply to Alizon and Michalakis. Evolution In press. doi:10.1111/j.1558-5646.2011.01428.x | Journal

Abstract: In a recent study of the symbiosis between bacteria and plasmids, the available evidence suggests that experimental evolution of plasmid virulence was primarily driven by within-host competition caused by superinfection. The data do not exclude the possibility, however, that a trade-off between virulence and infectious transmission to uninfected bacteria also played a minor role.

This one’s an in-print discussion between Samuel Alizon, Yannis Michalakis, and myself. They were worried that some researchers might interpret my earlier paper about plasmid evolution as rejecting the hypothesis that pathogen virulence can be influenced by a trade-off between infectious transmission and virulence. So they made some mathematical models to determine what kinds of evidence we’d need to really rule out the influence of such a trade-off. The work I did doesn’t rule out a trade-off, but it does show that competition among pathogens within hosts was necessary and sufficient to explain how plasmid virulence evolved.

I found it nice (and useful) to talk with the authors before we sent in our respective manuscripts. It helped clear up some places where we were using language in a way that could be misinterpreted and to focus on places where there might be real issues. In the end, my impression is that we basically agree about what my paper does and doesn’t show, but they wanted to use it as a sounding board for how we should go about testing virulence theory.

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